Method of and apparatus for bleaching pulp



R. B. WOLF.

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- R. B. WOLF. METHOD 0F AND APPARATUS FDR BLEACHING PULP. APPLICATION FILED MAR. I3. 1922. 1.433.865., Patented 00AM, T922.,

4 SHEETS-SHEET 2.

INVENTOR.

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R. B. WOLF.

METHOD 0F AND APPARATUS FOR BLEACHING PULP.

APPLzcATxoN FILED MAR.13.1922. L Patented @011311,1922

4 SHEETS-$11551 a.

WNTOR [Bx/@Qu a LW/1 ,41 ATTORNEYS RfB. WOLF.

METHOD 0F AND APPARATUS FOR BLEACHING PULP.

APPLICATION FILED MAR 13, 1922.

L rammed oet. 311, 1922 4 SHEETS-SHEET 4.

m.; ATTORNEYS mi? v n? INVENTOR Patented ct. 31, 1922.

sTATEs ROBERT IIB. WOLF, OF NEW YORK, N. Y.

METHOD OF AND APPARATUS FOR BLEACHING PULP.

. Application filed March 13, 1922. Serial'No. 543,234.

To all whom t may concern:

Be it known that I, ROBERT B. WOLF, a citizen of the United States, residing at New York city, in the county of New York, State of New York, have invented certain new and useful Improvements in Methods of and Apparatus for Bleaching Pulp; and I do hereby declare thefollowing to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. l

This invention relates to the bleaching of pulp or paper stock, and particularly to a' method of and apparatus for treating such material to more effectively accomplish the desired bleaching.

In the bleaching of paper stock it has been proposed heretofore to treat the materialin apparatus including, for example, a horizontal tank having a medial partition or midfeather about which the mixture of pulp and bleaching liquor is caused to sluggishly circulate by one or more transverselyarranged propellers. Other forms of apparatus `have been used for this purpose. In all such apparatus the maximum permisvsible-concentration of the pulp is approximately 6%, at which concentration the mass Vis substantially fluid. This low concentration is necessary because of the difficulty otherwise experienced in maintaining the desired circulation. Moreover, the temperature of the mass must be relatively high, e. g., 110 F. to ensure the desired bleachin action within a reasonable time.

Aside from the slowness of the bleaching operation which consumes approximately eight hours, the additional difficulty is presented that the relatively high temperature tends to break down the cellulose, thus causing a greater loss in bleaching than would result from an operation conducted at a lower temperature. Furthermore, the discolored fibres commence to bleach too rapidly on the outside and the bleaching solution is thereby prevented from penetrating the fibre and thoroughly bleaching'the same.

I have discovered that the bleaching operation may be more effectively conducted with several advantages, including those hereinafter set forth, by employing a mass of pulp and bleaching agent of much higher concentration than has heretofore been practicable. Thus the vmass may contain agent is mechanically advanced and periodically agitated to ensure thorough commingling of the pulp and bleaching agent. With the higher concentration of pulp a bleaching solution containing 20 to 30 grams of available chlorine per liter may be used. The operation may be conducted at a lower temperature than heretofore, and shrinkage, which would otherwise result from the breaking down of the cellulose, is thereby avoided. As a result of operation in the manner described, it is possible tomaterially increase the effectiveness of bleaching operations so that a mass containing, for example, 18 to 20% of pulp may be successfully bleached in about three hours or less than half the time required under the old practice using a mass containing not over 6% of pul'p.

Il have discovered also that the pulp may be advantageously delivered directly from the wet machine to the bleachers. This operation is particularly desirable inasmuch as it facilitates the removal of moisture to a degree -which ensures a pulp mass of the desired concentration when the bleaching agent is added. In the wet machine the pulp ispreferably concentrated to about 25 to 30% and is delivered directly from the doctor tothe bleachers where it is mixed with sufiicient bleaching liquor to provide a mass containing, for example, 18 to 20% of pulp. A plurality of bleaching tanks may be provided so that the capacity of the bleachers equals that of the we t machlne.

As a result ofthe high concentration of pulp in the mass, there is a tendency to the formation of fish eyes, i. e'., small globular bodies formed by the agglomeration of the fibre. These bodies, if permitted to remain, would interfere with the production of paper from. the pulp. I have discovered-however, that byldilution of the pulp and passage thereof over rif'fies the-fish'eyes may be entirely eliminatedf. The pulp is thus prepared for its utilization in the manufacture of paper.

Fig 3 is a side elevation of the same ap-I paratus;

Figl is a plan view with the cover removed of another form of the invention;

Fig. 5 is a plan View of vanother form of the invention;

Fig. 6 diagrammatically illustrates the arrangement of the Wet machine and vthe bleachers, whereby the pulp is delivered direc-tly to the bleachers;

Fig. 7 is a plan view of another type of bleaching tank;

Fig. 8 is a vertical section through the structure illustrated in 7 and Fig. 9 diagrammatically illustrates the arrangement of the riiiies with reference to the bleaching apparatus.

In the accompanying drawings, I have illustrated an oblong tank having the vertical side walls 10, 11 and end walls 12, 13. Midway between the side walls there is a vertical partition or midfeather 14 which extends between the end walls 12 and 13 and around which the pulp is to be fed. At its ends, the midfeather is provided with large there are located ianged metal bushings 16.

Extending axially through the two ports are shafts 17, 18, which are journaled in suitable bearings mounted.; in the side walls 10 and 11 of the tank and provided with stuling boxes or other suitable devices to prevent leakage of the contents of the tank. On the shafts 17 and 18 there are short worm propellers or agitators 19 and 20 which t within the collar 16. The shafts 17 and 18 carry also reverse propeller blades 19 to prevent piling of the mass against the sidesl ot' the tank. The ports 15 are located some distance below the upper edge of the midfeather so that the propellers are submerged in the contents of the tank. The shafts 17 and 18 may be driven in any suitable way, for example, by electric motors 21, 22, the shafts of which are connected to the shafts 17 and 18 by suitable power-transmitting mechanism. The motor shafts may, for example, have the small sprockets 23 from whlch chains 21 extend to the Sprocket wheels25 on the propellenbearing shafts. If these shafts are driven in the same direction, the worm; propellers are of opposite hand or pitch, but, if driven in the oppositedirection as shown, the propellers are of the same hand or pitch, the purpose being to transfer the stock from one side of the midfeather and at the same time to effect thorough commingling of the fiber and the aqueous bleaching solution.

In accordance with the present invention for accomplishing the purposes which I have hereinbefore stated, I provide means extending longitudinally of the tank for mechanically conveying the stock ina closed path through the tank, as a result of which I am y able to use a muchy more concentrated pulp mass which could not be successfully treated otherwise. Thus, in the lower part of each of the longitudinal compartments formed in the tank by the midfeather 14, I provide pairs of worm propellers of opposite hand, A

as clearly shown in Fig. 1. The worm propellers of each pair are indicated at 26, 27, and their shafts 28, 29 are ournaled in suitable bearings in the end walls 12 and 13. The bottom of each compartment is preferably formed with semi-cylindrical grooves or beds 30, 31 to receive the worm propellers as shown in Fig. 2. The shafts 28 and 29 at one end project beyond the end wall 13 and aredriven in anv suitable manner. For example, I employ an electric motor 32, which through pinion 33 and gear V311, drives a shaft 35 having suitable driving connections cooperating .with and driving worm gears 36 on the shafts 28 and 29. 1

The worm propellers or conveyers are rotated at` relatively slow speed, those of Aeach pair being rotated in opposite directions so as to vfeed the whole body of stock slowly around the'midfeather and constitute with the material in which the conveyers are embedded a moving bottom of the two compartments of the tank upon which the bulk of the mass of pulp and bleaching agent is bodily transported. Shafts 17 and 18, on the other hand, are driven at relatively higher speed so that the fanlike propellers or short worms offer comparatively little resistance to the stock and yet furnish the necessary mixing or brushing action to thoroughly mix the bleaching reagent with thel pulp. To assist in breaking up and more effectively mixing the pulp with the bleaching reagent, there is placed on one end of each of the shafts 28, 29 a short lworm blade or A stock upwardly when it reaches the end of the compartment and' also to break up lumps of pulp.

Referring to Fig. 6 of the drawing, the wet machine is indicated at 59 and is supplied with pulp through a pipe 60. The wet machine is provided with rolls 61 and 62 and a traveling felt 63 supported on idlers 64 and adapted to convey the pulp to a doctor 65. The latter delivers the pulp to a trough 66 having a worm conveyer 67 therein. The trough is disposed with re spect to one or more of the bleaching tanks so that the pulp may be delivered directly to the tanks as desired. This arrangement effects a material saving in the handling of the pulp and enables the production of a drier pulp and a more uniform mixture of the pulp with the bleaching liquor than is otherwise possible.

In operation, the pulp, for example, from the wet machine, and the bleaching liquor are fed into the tank in any convenient way and the various moving parts are set in operation. The longitudinally arranged worms are rotated slowly, say from 4 to 6 revolutions per minute, and the cross propellers or worms are driven at relatively high speed, say 5() to 100 revolutions per minute. The whole dense mass travels bodily through each compartment under the propelling action of the longitudinal worms, the cross worms agitating and mixing the pulp with the reagent as the mixture passes from one compartment to the other.

As hereinbefore noted, the treatment of the concentrated mass of pulp sometimes results in the formation of fish eyes in the mass. This difficulty may, however, be readily overcome. Referring to Fig. 9 of the drawing, a bleaching tank 68 is diagrammatically illustrated, the tank being provided with means such as longitudinal worms 69 to advance the body of pulp therethrough and with transversely-disposed worms 70 for the purpose of agitating the pulp. The pulp in this tank is relatively concentrated, e. g., 18%. At the conclusion of the bleaching operation, the pulp is dis charged through a pipe 71 controlled by a valve 7 2 to a drainer 73 having a perforated bottom 74. In the drainer the bleach liquor '1s separated from the pulp which is then washed with water supplied through a perforated pipe 75. The bleaching liquor and the wash water are discharged through a ipe`76. Then the washing has been com pleted, the pulp is flushed out of the drainer by water supplied through a pipe 77 and is delivered through a pipe 78 and pump 79 to a storage tank 80. Owing to the ad dition of water in flushing the drainer, the pulp in the storage tank 80 is much less concentrated, e. g., 2 to 3%- From the storage tank the pulp is discharged through a pipe 81, pump l82 and pipe 83 to the head of the riffler 84 where it enters a box 85 and is mixed with water supplied through a pipe 86. Sufficient water is added to reduce the concentration preferably to approximately of 1%. The mixture of pulp and water overflbws a baffle 87 and thence passes over baffles 88 and 89 onto a table which is covered with a suitable material, preferably a cotton felt having upwardly extending fibres which serve to catch the pulp fibre and permit separation thereof as the material fiows over the table. Owing to the dilution and the action of the riffler, any fish eyes present in the mass are disintegrated, and the pulp is delivered toa box 90 at the end of the Iriflier and thence through apipe 91 to the wet machine (not shown) where the water is again removed from the pulp. The pulp is thus reduced to a condition for use.

It is evident that. instead of having a single midfeather dividing the tank into two compartments, T may-employ a tank as shown in Fig. 5, in which there are two midfeathers 40,' 41, extending longitudinally of the tank and dividing it into three compartments. Tn such case, the stock is caused to flow first through the outer compartments and then in the opposite direction through the middle compartment. This outer compartments are provided with worms 42, 43, similar to those described in connection with the tank illustrated in Fig. 1, and having similar short reverse worm sections 422t and 43a at their ends. The middle compartment is provided with longitudinally arranged worms 44, 45, which are of opposite pitch and are driven in opposite directions so as to force the stock received at one end of the compartmentout from the other end thereof. These worms also have short reverse worm sections 44a and 45a at their ends. The two midfeathers 41. 4() are provided with ports or openings through which the shafts 46, 47 extend, and the said shafts are provided with short worm' propellers of proper pitch sov as to effect the lpassage of the stock from the outer com- -is secured thereby inasmuch as the end thrust of the vworm propellers on the shaft is neutralized, one by the other.

Instead of employing short transverse! worm propellers, the apparatus may be made as shown in Fig. 4, in which said propellers are omitted. In this case the midfeather has its ends spaced or separated from the end walls 51,51, of the tank to leave passageways 52, 52. I .utilize the longitudinally arranged worm propeller for circulating the body of the stock around the midfieather as shown by the arrows, but also so construct the worm conveyers or propellers that they shall have not only a feeding action but also an agitating or mixing action upon the stock. To this end, I employ in each compartment of the tank the two pairs of worm conveyers which are indicated as a whole at 53, 54. The shafts, on which these conveyers are formed or secured, are rotated in opposite directions by mechanism substantially asl described in connection with Fig. 1. The propellers 53 are provided with blades 55, the function of which is to feed the body of stock in the direction of the arrows longitudinally of the compartments. Between these blades 55 the conveyers have blades 56 which are of opposite pitch to those at 55 and which are less in number, the function of which is partially to interrupt the flow and force. the stock upwardly so as to effect a churning and agitating action thereon. The propellers 54 have blades 57 and 58 respectively arranged opposite the blades 55, 56, but of opposite pitch -inasmuch as the shaft on which they are mounted rotates -in the opposite direction to that in which the propeller53 is bodily rotated.

In Figs. 7 and 8 of the drawings, a different form of bleacher is illustratedawhich may be employed in place of the bleachers previously described. The -bleacher comprises a tank 92 preferably formed of tilelined Portland cement ,or other suitable material which is not affected bythe action of the bleach liquor and is preferably provided with a suitable cover. A midfeather 93 extends through the tank and is provided with openings 94 at opposite ends. Transverse shafts 95 are mounted in suitable bearings inthe walls of the tank and are provided externally with driving means adapted to be actuated from any suitable source of power. The shafts` 95 carry worms 96 which, when the shafts are actuated at relatively high speeds, serve to break up and agita-te the pulp which is passing. through the apparatus. Preferably `short worms 97 are provided nea-r the ends of the shafts 95 to prevent the material traversed from the opposite sides of the midfeather from piling up in the ends of the tank,

nsides of the tank.

To ensure movement of the concentrated pulp mass through the tank, a conveyer is provided which may consist of a plurality of chains 98 driven by suitable sprockets 99 and 100, the former being mounted on shafts 101 supported in brackets 102 above the tank, and the latter being mounted on shafts 103 supported in bearings in the The shafts 101 or 103 may be actuated from any suitable source of power to ensure the advance of the chains in the directions indicated by the arrows in Fig. 7. The chains form, therefore, a moving bottom for the tank which carries the concentrated pulp mass from one end to the other thereof. As the mass advances, the worms 96 churn the mass and pass it through the openings 94 inthe midfeather. The continued circulation ofthe mass bodily advancing through the tank and intermittently agitating results in a thorough action of the bleaching reagent in a relatively short space of time. in accordance with the principles of the invention. It is possible, with an apparatus such as described, to considerably more than double the proportion of the pulp in the mixture,

and it may be noted further that a pulp concentration of 6%, such as is customarily used, cannot be successfully treated in the apparatus described because of the iiuid character of such a mass. The wormy propellers in this case impede rather than facilitate the circulation. Instead of using a mixture-containing 6% ofthe pulp, I employ a mixture containing from 10 to 25% of pulp, and consequently increase correspondingly the concentration of-the calcium bisulphite in the aqueous solution. I am thus enabled to carry on the bleaching operation at a temperature not exceeding 75o to 80- F. The increased density of the mixture has the effect of'lowering the resistance to the action of the bleaching reagent upon the fibers, especially those containing a high amount of color pigments, so vthat a more thorough bleaching is effected with'consequent production of a whiter fibre. Moreover, the more gentle action of the reagent because of the lower temperature permits a greater yield of stronger'iibre since the-destruction of cellulose is practically negligible. Inasmuch as a smaller amount of vwater is required, and as the reaction is carried on at a lower temperature, much less water has to be heated, and Ihave attained in actual practice a reduction in the amount of fuel used to substantially one-eighth as much as is used in the former practice.

fVarious changes may be made in the details of the operation as hereinbefore described and within the scope of the accom panying claims without departing from the invention or sacrificing any of the advan tages thereof.

` I' claim: I

1. A method of` bleaching pulp, which comprises inixi'ngthe pulp with a bleaching agent, the concentration ofl the pulpbeing. .such as to provide a substantially nonfliuid subjecting it at intervals A'to agitation to eni i cent of the `-mass, mechanically conveying 'surethorough commingling of .the bleaching agent with the pulp. j l

@L A method of bleaching pulp, which comprises mixing the pulp With a bleaching agent, the pulp forming-more than`per the pulp mass andsubjecting it at 'intervals to agitation to ensure thorough commingling of the bjleachingagent With the pulp.

Y. 'i 5. Aniethod of bleaching pulp," which comprises mixing the pulp with a bleaching agent, ,the pulp forming more .than =1 0 per cent'o'f the mass, mechanically conveying the mess in a closed circuit and successively agi-l tating the mass as it travels;

'6. A method of bleaching pulp, which l 'comprises mixing the pulp -with a bleaching agent, maintaining the mass at a tempera-y ture not exceeding 80 lE`.,mechanically conveying the massin a closed circuit and suol cessively' agitatm'g' the mass during its` travel] e 7. A method "of bleaching pulp, which comprises mixing the pulp with a bleachingl agent and mechanically conveying the mass during the major portion of its travel, in a closed circuit.

8. Ae. method of Hechingen@ which comprises mechanically removing a portion of the moisture from the'mass so that the y mass will contain between 25 and 30 per cent of pulp," adding a proportion of a-,bleaching agent thereto and mechanically conveying the mass as ,1t is subjectedto the bleaching action.

y9. A method oi bleaching pulp which comprises mechanically removing a portion of moisture from the pulp, adding bleaching .agent thereto and mechanically conveying the mass during a portion of itstravel substantially Without agitation, and agitating the mass to ensure thorough commingling of the bleaching agent with the pulp.

' 10. A method of bleaching pulp,.vvhich ing said midfeather, and means at' the ends of comprises mixing the pulp with a bleaching agent, the concentration of the pulp being more thanv 1() per cent, and subjecting the mass to a temperature not exceeding 80o F. 4

11. Amethod of bleaching pulp, which comprises mixing the pulp with a bleaching agent, the concentration of the pulp being substantially 18 per cent, andsubjecting the `mass to a temperature not exceeding 80 F.

12. Av method of bleaching pulp, Which comprises mixingthe pulp With a bleaching agent, maintaining the mass at -a temperature not exceeding 8Oo F., causing the mass to travel -in a closed circuit' and agit-ating the mas-s during its travel.

13. A method of bleaching pulp, which comprises mechanically removing a portion of the moisture from the pulp, adding a proportion of a bleaching agent thereto, and subjecting the mass to a temperature not exceedinfr80 F l 14. method of bleaching pulp, "Which comprises mechanically removing a portion of the moisture-from the pulp, immediately adding bleaching agent thereto in proportion to provide a mass containing more tlian 10 per cent of pulp, and subjecting the mass tointermittent agitation to ensure thorough commingling of the bleaching agent With vthe pulp. `15. A method of bleaching pulp, which com'prisessubjecting the pulp to the action of a bleaching reagent, the concentration of the pulp being such as to provide a substantially non-fluid mass, and "thereafter diluting the pulp to4 alow concentration to ensure separation of agglomerated fibre.

16. A method of bleachingpulp, which comprises subjecting the pulp to the action of a bleaching rea-gent, the concentration of the pulp-.being such as to provide a Substantially non-fluid mass, diluting the pulp vto a low concentration and passing it over rilies to ensure separation of agglomerated libre.

17. Apparatus for bleaching paper pulp., comprising al tank 'having a midfeather; dividing it 'into longitudinal compartments, and conveyers arranged longitudinally of said compartments for bodily conveying a mixture of pulp and bleaching reagent containing more than 10 ,per cent of pulp about said midfeather. v

18. Apparatus for bleaching paper pulp,

.comprising a tank having a midfeather dividing it into longitudinal compartments, conveyers arrangedlongitudinally of said compartments for bodily conveying a mixture of pulp and bleaching reagent containmore than 10 per cent of pulp 'about the midfeather for agitating and intermingling the components of said mixture.

19.4 Apparatus vfor'bleacliing paperfpulp,

comprising a tank having a midea-ther dividing it into longitudinal compartments, the bottom of each compartment being Jformed with longitudinal grooves or beds, and helical conveye-rs arranged in said grooves or beds for .bodily conveying a mixture of pulp and bleaching reagent containing more than 10 per cent of pulp about said midfeather.

20. Apparatus for bleaching pulp, comprising a tankjhav'ing a midfeather dividing said tank into longitudinal compartments, a pair of helical conveyers in each compartment, said conveyers having opposingr blades of opposite pitch, the' conveyers in the two compartments being arranged to bodily convey a mixture ot' pulp and bleaching reagent containing more than l0 per cent o1 pulp in opposite directions so as to travel about the midfeather, and :means for rotating :the conveyers.

21. Apparatus for bleaching pulp, comprising a tank having a midteather dividing said tank into longitudinal compartments, a pair of helical conveyers in each compartment, said conveyers having opposing blades of opposite pitch, the conveyers in the ytwo compartments being arranged to bodily convey a mixture of pulp and bleaching reagent containing more than 10 per cent of pulp in opposite directions so as to travel about the midfeather, and at least one of each said conveyers -having blades opposite in pitch to the other blades thereof, to force the stock oppositely. j

22. Apparatus for blea'chino` pulp, eomprising a tank having a longitudinal mid.

feather dividing it into longitudinal compartments, said midfeather having ports or openings adjacent its ends, an agitator or propeller located in one of said openings, and means for rotating said agitator, in combination with means-in said longitudinal compartments for bodily conveying a mix#- ture of pulp and bleaching.- reagent contain'- ing more than 10 per cent of pulp about said midfeather. i

23. Apparatus for bleaching pulp, comture.

prising a tank having a longitudinal midfeather dividing it into longitudinal compartments, said midfeather having ports or openings adjacentits ends, an agitator or propeller located in each of said ports or openings to agitate the mixture passing therethrough, and conveyers arranged longitudinally of said compartments for bodily conveying a mixture of pulp and bleaching reagent'containing more than l() per cent of pulp about said midt'eather.

Apparatus forv bleaching pulp, comprislng a tank having a, longitudinal midi'eather dividing it into longitudinal compartments, said midteather having ports or openings adjacent its ends, an agitator or propeller located in each of said ports or openings lo agitate the mixture passing therethrough, helical conveyers arranged longitudinally oit said compartments for bodily conveying a mixture of pul'p and bleaching reagent containing more than 10 per "cent of pulp about said midfeather, inea-ns for rotating said worm conveyers at relatively slow speed, and means for rotating said agitators at relatively highspeed.

25. Apparatus for bleaching' pulp, c'omprising a tank having'at least one longitudinal midfeather`v dividing it into longitudinal compartments, said mid'leather or midleathers havingports or openings adjacent the ends, atleastone agitator or propeller located in each of- Said compartment, said propellers having helical blades ofr the same pitch throughout the greater part of their length and having short helical portions of opposite pitch at the discharge ends of the compartments adjacent the ports or openings.

2G. 1n apparatus for bleaching pulp, at least one helical conveyor at the bottom of a pulp compartment for agitating and conveying the pulp therein, and short sections of the 4helical conveyor of opposite pitch adjacent the end of the compartment.

In testimony whereof I aiiix my signa- RoBERT B. WOLF. 

